Systemic chemotherapy is one of the remaining avenues available to an oncologist treating unresectable non-small cell lung cancer (NSCLC). Unfortunately, NSCLC indicated anticancer therapeutics do not provide significant patient survival benefits and have toxic side effects. These drugs will extend the time-to-progression of metastatic disease by small margins yet do little to decrease NSCLC mortality. An underlying theme to the current proposal is that one can obtain significant improvements in NSCLC chemotherapy with a more detailed molecular understanding of drug disposition and response. To obtain this understanding we will use a combination of structural biology and functional assays to study a human integral membrane protein directly linked to gemcitabine uptake within normal and neoplastic cells. The equilibrative nucleoside transporter (hENT) family is broadly distributed in human tissues, is known to transport a wide array of nucleoside antimetabolites, and is directly linked to chemotherapeutic outcomes. Specific goals we seek to address in this proposal include (1) determine the structure of hENT at atomic resolution, (2) develop in vitro functional assays using purified protein, and (3) characterize hENT functional determinants using three human lung cancer cell lines. Outcomes from these studies will be tuned to determine the molecular basis by which hENT regulatoin and transport of therapeutics occus. The broad vision is that these novel molecular insights can be advanced to clinical outcomes that guide treatment decisions in nucleoside based drug treatment of NSCLC.